1. Field of the Invention
The present invention relates to an arteriosclerosis evaluating apparatus for evaluating arteriosclerosis based on augmentation index.
2. Related Art Statement
Augmentation index, AI, is generally calculated as a percentage of a value obtained by deriving a difference between a magnitude of a peak of a pulse wave (i.e., a pulse pressure of the pulse wave) and a magnitude of a peak of an incident-wave component contained in the pulse wave (i.e., a pulse pressure of the incident wave), by the pulse pressure of the pulse wave. Since the augmentation index increases as arteriosclerosis advances, the augmentation index can be used as an index for evaluating arteriosclerosis.
However, the augmentation index is influenced by physiological factors, such as blood pressure or psychological stress, and environmental factors such as temperature, and accordingly the augmentation index may largely change between different living subjects, or between different measuring operations. Thus, a correlation between augmentation index and arteriosclerosis is not so high. Therefore, it is understood that arteriosclerosis cannot be evaluated based on augmentation index only.
It is therefore an object of the present invention to provide an arteriosclerosis evaluating apparatus for evaluating arteriosclerosis of a living subject, with high accuracy, based on augmentation index.
To achieve the above object, the Inventor has carried out extensive studies, and found the following facts: It is known that as arteriosclerosis advances, respective waveforms of respective pulse waves detected from different portions of a living subject become more and more similar to each other. Based on this knowledge, the Inventor have found that as arteriosclerosis advances, respective augmentation indexes calculated from the respective waveforms of the respective pulse waves gradually approach each other, and that arteriosclerosis can be evaluated by comparing the respective augmentation indexes of the different portions of the subject, with each other. Since those augmentation indexes are subject to common physiological changes and common environmental factors, arteriosclerosis can be evaluated with high accuracy by comparing those augmentation indexes with each other. The present invention has been developed based on these findings.
The above object has been achieved by the present invention. According to a first aspect of the present invention, there is provided an apparatus for evaluating arteriosclerosis of a living subject, comprising a pulse-wave detecting device which detects a pulse wave from each of a first portion and a second portion of the subject, each of the respective pulse waves detected from the first and second portions containing an incident-wave component; an augmentation-index determining means for determining, based on the pulse wave detected from the first portion by the pulse-wave detecting device, a first augmentation index indicative of a degree of augmentation of an amplitude of the pulse wave detected from the first portion, from an amplitude of the incident-wave component of the pulse wave detected from the first portion, and determining, based on the pulse wave detected from the second portion by the pulse-wave detecting device, a second augmentation index indicative of a degree of augmentation of an amplitude of the pulse wave detected from the second portion, from an amplitude of the incident-wave component of the pulse wave detected from the second portion; and an arteriosclerosis evaluating means for evaluating the arteriosclerosis of the subject, based on a comparison of the first and second augmentation indexes determined by the augmentation-index determining means.
According to this invention, the augmentation-index, determining means determines the respective augmentation indexes of the different portions of the living subject, and the arteriosclerosis evaluating means evaluates arteriosclerosis of the subject, based on the comparison of those augmentation indexes of the different portions. That is, since the present apparatus evaluates arteriosclerosis by comparing the plurality of augmentation indexes obtained from the single subject, with each other, the physiological changes and the environmental factors that influence those augmentation indexes are offset, and accordingly the arteriosclerosis can be evaluated with higher accuracy than the evaluation of arteriosclerosis based on a single augmentation index only.
Preferably, the arteriosclerosis evaluating apparatus further comprises a comparison-value calculating means for calculating a comparison value as the comparison of the first and second augmentation indexes determined by the augmentation-index determining means, and the arteriosclerosis evaluating means evaluates the arteriosclerosis of the subject, based on the comparison value calculated by the comparison-value calculating means and at least one of the first and second augmentation indexes determined by the augmentation-index determining means.
According to this feature, arteriosclerosis can be evaluated with improved accuracy, because at least one augmentation index itself is taken into account in addition to the comparison value as the comparison of the first and second augmentation indexes of the different portions of the living subject.
Preferably, the arteriosclerosis evaluating apparatus further comprises a comparison-value calculating means for calculating a comparison value as the comparison of the first and second augmentation indexes determined by the augmentation-index determining means; and a pulse-wave-propagation-velocity-related-information obtaining device which obtains pulse-wave-propagation-velocity-related information that is related to a velocity at which the pulse wave propagates in the subject, and the arteriosclerosis evaluating means evaluates the arteriosclerosis of the subject, based on the comparison value calculated by the comparison-value calculating means and the pulse-wave-propagation-velocity-related information obtained by the pulse-wave-propagation-velocity-related-information obtaining device.
According to this feature, arteriosclerosis can be evaluated with improved accuracy, because the pulse-wave-propagation-velocity-related information that is, like augmentation index, an index indicative of arteriosclerosis is taken into account in addition to the comparison value as the comparison of the first and second augmentation indexes of the different portions of the living subject.
Preferably, the arteriosclerosis evaluating apparatus further comprises a comparison-value calculating means for calculating a comparison value as the comparison of the first and second augmentation indexes determined by the augmentation-index determining means; and a pulse-pressure determining means for determining a pulse pressure of at least one of the respective pulse waves detected from the first and second portions by the pulse-wave detecting device, and the arteriosclerosis evaluating means evaluates the arteriosclerosis of the subject, based on the comparison value calculated by the comparison-value calculating means and the pulse pressure determined by the pulse-pressure determining means.
According to this feature, arteriosclerosis can be evaluated with improved accuracy, because the pulse pressure that is indicative of arteriosclerosis is taken into account in addition to the comparison value as the comparison of the first and second augmentation indexes of the different portions of the living subject.
According to a second aspect of the present invention, there is provided an apparatus for evaluating arteriosclerosis of a living subject, comprising a pulse-wave detecting device which detects a pulse wave from each of a first portion and a second portion of the subject, each of the respective pulse waves detected from the first and second portions containing an incident-wave component; an augmentation-index determining means for determining, based on the pulse wave detected from the first portion by the pulse-wave detecting device, a first augmentation index indicative of a degree of augmentation of an amplitude of the pulse wave detected from the first portion, from an amplitude of the incident-wave component of the pulse wave detected from the first portion, and determining, based on the pulse wave detected from the second portion by the pulse-wave detecting device, a second augmentation index indicative of a degree of augmentation of an amplitude of the pulse wave detected from the second portion, from an amplitude of the incident-wave component of the pulse wave detected from the second portion; and a display device which displays the first and second augmentation indexes determined by the augmentation-index determining means.
According to this invention, the augmentation-index determining means determines the respective augmentation indexes of the different portions of the living subject, and the display device displays the respective augmentation indexes of the different portions. Thus, a person can judge, from comparison of the respective augmentation indexes displayed, that the nearer those augmentation index values are to each other, the higher the degree of arteriosclerosis is; and that the more distant the augmentation index values are from each other, the lower the degree of arteriosclerosis is. Thus, arteriosclerosis can be evaluated with higher accuracy than the evaluation of arteriosclerosis based on a single augmentation index only.